The present invention relates to an internal combustion engine which includes a high pressure fuel pump for supplying a high pressure fuel and fuel injectors and more particularly, to a control apparatus for such an internal combustion engine (which will be referred to as an engine, hereinafter) which can reliably reduce a fuel pressure in high pressure fuel pipe.
Such an engine of a cylinder injection type as to directly inject a high pressure fuel into a cylinder is already known. The fuel is forcedly supplied to the engine by a low pressure fuel pump provided to a fuel tank of a vehicle. The engine is provided with a high pressure fuel pump, the supplied fuel is further compressed to a high pressure by a driving force from the engine, and then supplied to high pressure fuel pipe having fuel injectors mounted thereto.
In recent years, there is such a demand as to increase a discharge efficiency of a high pressure fuel pump, decrease a friction and make the fuel pump compact and light in weight. In order to meet such a demand, a high pressure fuel pump for adjusting a discharged fuel quantity by controlling a charged fuel quantity has been developed. In this type of high pressure fuel pump, the sucked fuel quantity is controlled by supplying a drive current from a control apparatus of the engine to a solenoid to drive a suction valve.
In such a high pressure fuel pump, when a wire harness for supplying a drive current to the inlet value is broken, control of the inlet value becomes disabled. This is considered to lead to such a situation that the high pressure fuel pump rotatingly driven by the engine supplies an excessive fuel to the high pressure fuel pipe. However, since the high pressure fuel pump or the high pressure fuel pipe is provided with a safety or relief value, the pressure of the fuel will not be increased beyond an valve opening pressure of the relief value, so long as the relief value is put in its normal state.
In a system including the high pressure fuel pump, if any abnormality takes place in the aforementioned relief valve, then it becomes necessary to secure a safety of the system by quickly suppressing an increase in the fuel pressure.
Meanwhile, when abnormal high pressure state continues for a period of a predetermined time as when a fuel pressure in a common rail is higher than a first judgement value corresponding to an allowable pump use limit or as when the fuel pressure is higher than the first judgement value and exceeds such a second judgement value as to cause deterioration of the performance of a fuel supply pump; an abnormality failure in the fuel supply pump is detected. Such a system as to stop an engine after passage of a predetermined time from a time point of detection of an abnormality failure in a fuel supply pump, is already known (for example, refer to Japanese Patent No. 3972823).
It is also known that, when a pressure in fuel within the high pressure fuel pipe at the downstream side of the high pressure fuel pump is detected by a fuel pressure sensor and is at an abnormal level higher than a predetermined pressure, the system is arranged to stop a field pump as a low pressure fuel pump, thereby reliably reducing the internal pressure of the high pressure fuel pipe (refer to Japanese Patent No. 3237567).